Arrangement for establishing time intervals



Patented Sept. 17,

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IRVING W. GREEN, 01 NET/V JERSEY, ASSIGNOZZ TO AMERICAN: TELE- PHONE ANDTELEGRAPH COMPANY, QORPORATIGN (333 NEXT? ARRANGEMENT FORESTAB'LTSI-IING TIBET; INTERVALS [application filed July 1, 1926.

ical characteristics of a vacuum tube therefor.

One of the objects of the invention is to provide arrangements forpreventing the flow of current in a circuit during a fixed interval oftime.

Another object of the invention is to provide a vacuum tube of suitableconstruction for automatically maintaining a signal at the subscribersstation of a telephone system for a fixed period or time after a ring-'ing signal has been transmitted from the central oiiice to thesubscribers station.

Uther objects of the invention will appear in the detailed descriptionto be given hereinafter.

A three-electrode vacuum tube consists essentially of a highly evacuatedvessel, containing a themionic cathode, usually in the form of afilament, which can be heated by passing a current through it, an anodeand a discharge controlling electrode which generally takes the form ofa wire mesh or grid placed between the cathode and the anode. Thisthird-electrode can, however, be of any form, since a controlling efiecton the discharge can be obtained by so positioning any conductor withrespect to the path of the discharge that potential variations appliedto it will cause variations in the current flowing between the cathodeandthe anode.

It has been found in the three-electrode vacuum tube employed in thearrangement described hereinafter that when a high potential is appliedto the grid of the vacuum tube, which makes the grid highly positivewith respect to the filament, there is a temporary increase in the flowof current between the plate and the filament, and then a suddendecrease in this current to a value considerably below the normal value.This cessation or diminution of the electronic emission between thecathode and the anode may exist for a considerable period of time, forexample, several minutes after the positive potential has been releasedfrom the Serial No. 119,973.

grid of the vacuum tube. This interval of time may be adjusted bychanging the potentials applied to the elements of the vacuum tube, andby changing the constants of the associated circuits. A vacuum tube onhibiting such features is shown in a copending application of H. A.Pidgeon, Serial No. 136,205, filed September 18, 1926, and such a tubewill be more fully described hereinarter.

This invention may now be more fully un-- derstood from the descriptionthereof hereinatter following when read in connection with theaccompanying drawing, in which Figure 1 indicates schematically acircuit arrangement embodying the principles of this invention, and inwhich Fig. 2 represents a characteristic curve of the vacuum tubeemployed herein, given so as to aid in an understanding of its theory ofoperation.

Referring to Fig. 1, a three-electrode vacuum tube V is shown, of thetype to which referencehas been made, this tube consistin of a grid, aplate and a filament. The reference character S represents an indicator,such as a lamp, located at the subscribers station which provides forthe subscriber a visual means to observe for a fixed and predeterminedtime thereafter that a ringing signal has been transmitted to hisstation. Ringing current applied to a telephone line L will energize thewinding a of relay This ringing current may be impressed upon thetelephone line L at a central oii ice (not shown), this ringing ciirrentflowing over the conductors of the telephone line L through the windinga of the relay l) and through the condenser C. As the winding a of therelay D becomes energized, its armatures 1 and 2 are attracted, whicharmatures move synchronously, being connected by a bar of insulation. Asthe armature of the relay D closes its contact, current flows from abattery 18, through the winding of a relay E, the winding 6 of the relayD, the armature 1 of the relay D, the filament or the vacuum tube V, thewinding of a relay l conductor 21, the armature of relay G and ground.Thus, current flows from the battery B through the filament of thevacuum tube V, heating said filament to an electron emittingtemperature. The grid of the vacuum tube V is brought to a suitablenegative potential with respect to the filament thereof, the circuitinterconnecting the grid and the filament, including a battery 13,, thearmature of relay H and conductor 22. With the potential of battery Bapplied to the grid ofthe vacuum tube V, normal current flows betweenthe plate and filament of the vacuum tube V from a battery 13,, thecircuit through which this current flows including the battery 13,, thearmature of relay J, the plate and filament of the vacuum tube V and aconductor 23.

As-soon as ringing current is applied to the telephone line L, thewinding of relay E becomes energized, attracting its armature. Currentthen flows from the battery 13 through the armature of the relay E andthrough the indicating device S, which indicating device is shown inthis invention in the form of a lamp, merely for the purpose ofillustration. The relay F is preferably a slow acting relay so that itswinding does not become fully energized to attract its armatures until apredetermined period of time after the potential of the battery B hasbeen applied thereto, thereby, allowlng the filament of the vacuum tubeto reach its normal electron emitting temperature. After thispredetermined period of time has elapsed, the armatures of relay F areattracted so that current flows from battery 13, through the armature 1of the relay F and its contact, conductor 24 and the winding of relay H.

The armature of relay H is attracted because of the flow of currentthrough the winding thereof from battery 13,, relay H remaining enerized merely momentarily by virtue of the make before break feature ofthe contacts associated with the armature of relay F. Another battery Bis temporarily connected in series relationshi with battery B betweenthe grid and the lament of the vacuum tube V, thus momentarily renderingthe grid highly positive with respect to the filament. The circuitinterconnecting the grid and filament of the vacuum tube V ,during thismomentary period includes battery 13,, armature 20f the relay D, battery3,, a resistance R and conductor 22. A temporary increase in a flow ofcurrent from the battery B, through the plate circuit of the vacuum tubeV then takes place. This increase in the flow of current lasts only fora very short period of time and thereafter drops considerably below thenormal plate current value, the current in the plate circuit, thecurrent in the plate circuit gradually building up to its normal value,a fixed and predetermined period of time after the highly positivepotential of the vacuum tube V has been removed from the grid. Thisfixed and predetermined period of time may be; by example, severalminutes. Moreover, this period of time may be varied by changing thepotentials applied to the elements of the vacuum tube V, or by changingthe constants of the various circuits associated therewith.

Upon the closure of armature 2 of the relay F because of the flow ofcurrent of definite magnitude from the battery B through-the windingthereof, a circuit including the winding of relay J becomes closed. Thislatter circuit includes battery B the winding of relay J, armature 2 ofrelay F, conductor 21, the armature of relay G and ground. Inasmuch asrelay J, as employed herein, is a slow acting relay, it is apredetermined period of time after the potential of the battery B hasbeen applied to the winding thereof that normal current may flowthercthrough, this period of time being the time required for thecurrent in the plate circuit to reach its minimum value. The armature ofrelay J is then attracted so that the potential for the plate of thevacuum tube V may be supplied by battery B through the winding of relayG. When the current in the plate circuit of the vacuum tube V is at itsminimum value, the energization of the relay G is insufficient toattract its armature. Yet,'after the normal current in the plate circuithas been built up (which may be several minutes later), the energizationof relay G will become sufiicient to attract its armature so that thegeneral ground connection provided by said armature is broken, therebydeenergizing the winding b of the relay D and the windings of relays E,F and J. The circuit arrangement is then ready, for its next operation.Thus, the embodiment of the invention shown in Fig. 1 is employed tooperate a visual signal S at a substation for a fixed and predeterminedperiod of time after ringing current has been applied to the telephoneline of the substation.

The explanation of the operation of the vacuum tube of this invention toproduce what is believed to be a blocking or paralyzing effect will bedescribed in connection with Fig. 2. When a potential is applied to thegrid of the vacuum tube which makes the grid highly positive withrespect to the filament, a flow of electrons is established from'thefilament to the grid. Due to the bombardment of the grid by theseelectrons, at a high velocity, the contact potential between thefilament and the grid is changed so that when the positive potential isremoved from the grid the effective potential of the grid is morenegative than it was before the positive potential was impresesdthereon. Thus the current flowing in the menace output circuit isreduced to a value consider ably below its normal value. This may, 'lpreferred, be considered the result of shift in the contact potentialbetween the grid and the filament, and will be better understood fromthe following description in connection with the characteristic platecurrentgrid voltage curve of the vacuum tube.

The grid oft-this vacuum tube is normally maintained at a suitablenegative potential 00 to give a corresponding plate current 0d. vVhen apotential is applied to the grid which makes the grid highly positivewith respect to the filament, the potential of the grid is in efiectmomentarily raised to a value, such as 0c, giving the plate current 09'.However, this eliectively increased grid potential causes a flow ofelectrons from the filament to the grid, which produces a change in thecontact potential between the filament and the grid, making the gridmore negative. Consequently the net effective grid potential is reducedby an amount such as he, sothat the grid potential assumes a.

value corresponding to ob, giving a plate current of oj. l/Vhen the highpotential is removed from the grid the effective grid potential becomes07a, thus rendering the potential of the grid With respect to theiilarnent lower than its original value 00 by an amount ck, which isequal to he. This results in a drop in the plate current to the value 0mshortly after the positive potential has been removed from the grid. I

The grid of the vacuum tube remains substantially at potential 07': withrespect to the filament for some time and then slowly drifts back to itsoriginal value 00, as is shown by the curve in which grid voltage isplotted against time. The etlect of the shift on the contact potentialmay be due either to the peculiar characteristic of the alloy core ofthe filament or to the characteristic of such a core when covered with athick shaggy coating of thermionically ac tive material. Yet, a morecomplete explanation of the cause for the shift in the corn tactpotential is not deemed necessary to an understanding of the invention.

ll hile this invention has been shown in one particular embodimentmerely tor the purpose of illustration,- it Will be understood that thegeneral principles of this invention may be applied to other and Widelyvaried organizations Without departing trom the spirit of the inventionor the scope of the appended claims.

What is claimed is:

1. An arrangement for establishing a cessation of current flow in anelectrical circuit for a predetermined time interval, comprising avacuum tube of the three-electrode type, means whereby the grid ismomentarily made highly positive With respect to the filament, and meansfor releasing said highly positive potatial from said grid, the filamentbeing unable to assume its normal electronic emission to the plate untila predetermined interval of time has elapsed after the hi hly posit vepotential has been removed t m the id.

2. The method 0 establishing an interval of time which consists inimpressing a highly positive po ntial on the grid of a three-electrodedisc e tube, and releasing said potential when the interval of time isto begin so that the normal conductivity between the plate and thefilament is greatly altered during said interval oil time.

3. The method of preventing flow of urrent in an electrical circuitwhich consists in impressing a highly positive potential on the grid inhe input circuit of a three-electrode vacuum tube, the output circuit ofwhich is associated with the circuit to be affected, ant releasing thehighly positive potential from the grid 'so that the flow of current insaid electrical circuit cannot take place until predetermined intervalof time has elapsed to permit the filament to resume its normal state orelectronic emission.

The method of substantially altering the normal flow of current in theoutput circuit of a three-electrode vacuum tube which consists inimpressing a highly positive potential on the grid in the input circuitof said tube, and releasing the grid from the effect of the highlypositive potential so that the flow of current in the output circuit issubstantially altered during the predetermined interval required'tor'the filament to resume its normal electronic emission to the plate.

5. lln a system for establishing a time in terval, in combination, aline, a ringer,

electrical discharge tube having input andoutput circuits, a source ofhigh potential, a signaling device, means associated with said line forconnecting said source of high potential to the grid in the. inputcircuit so as to make the grid highly positive with respect to thefilament when a ringing signal is being transmitted over said line tothe said ringer, and means to operatively connect said signaling deviceduring the interval of time required for the filament to reach thenormal state of electronic emission to the plate after said source ofhigh potential has been removed from the grid.

6. In a ringing system, in combination, a line having a ringerassociated therewith, a discharge tube having grid, plate and filament,an indicator, means for impressinga potential onthe grid of said tube soas to make said grid highly positive with respect to said filament, andcircuit means opera-- tively associated with the plate circuit of saidtube to operate said indicator during the time that ringing current isbeing transmitted and during the interval of time thereafter in whichthe normal state of electronic emission of the filament to the plate isimpaired.

7 The method of establishing a time interval which consists in makingthe grid of an electrical discharge tube highly positive with respect tothe filament, operating an indicator during the time that said rid ishighly positive, and keeping said in iicator in operation during theinterval of time that it takes the filament to reach its normal state ofelectronic emission after the potential is removed from the grid of saidtube.

8. The method of producing a time interval in the flow-of currentthrough an electrical circuit with which a three-element vacuum tube isassociated, which consists in rendering the grid electrode normallynegative with respect to the filament so that there may be a normalstate of electronic emission between said filament and the plateelectrode, and changing the potential so as to render the grid electrodehighly positive with respect to the filan'ient in order to prevent thenormal electronic emission between the filament and the plate electrode,whereby the normal flow of current through the electrical circuitassociated with the vacuum tube may be greatly decreased during apredetermined interval of time.

9. The combination of a vacuum tube system having plate, filament andgrid electrodes, a transmission circuit connected to said plate andfilament electrodes, means to render the grid electrode normallynegative with respect to the filament electrode, and means to releasethe grid electrode from its normal negative potential with respect tothe filament electrode and to render said grid electrode highly positivewith respect to said filament electrode, whereby the normal electronicemission between the plate and filament electrodes is greatlydiminished, causing a cessation in the flow of current through saidtransmission circuit.

In testimony whereof, I have signed my name to this specification this29th day of J une, 1926.

IRVING WV. GREEN.

